1. Field of the Invention
The present invention relates to an optical-reading type image detector comprising a plurality of linear electrodes laid out in a stripe like-shape for obtaining an electric signal in accordance with the amount of latent image charge.
2. Description of the Related Art
Apparatus using image detectors, such as fax machines, copiers, and radiation image recording apparatus have been known.
In radiography for medical diagnoses for example, various kinds of methods and apparatuses using solid-state radiation detectors (electrostatic recording material) as image detectors have been proposed and put into practice. In a solid-state radiation detector, an electric charge obtained by detecting radiation is stored in a capacitor as a latent image charge and the latent image charge having been stored is output after being converted into an electric signal representing radiation image information. As a solid-state radiation detector used in such a method and apparatus, various kinds have been proposed. In terms of an electric-charge reading process for detecting a signal having a magnitude corresponding to the amount of the latent image charge having been stored, optical-reading type detectors on which reading light (an electromagnetic wave for reading) is irradiated are known.
There have been proposed optical-reading type solid-state radiation detectors enabling both fast response upon reading and efficient output of signal electric charge in Japanese Patent Application Nos. 10(1998)-271374, 11(1999)-87922, 11(1999)-89553, and 11(1999)-207283, for example. A detector described therein comprises a first electrode layer (conductive layer) having transparency to recording radiation representing image information or to light emitted by excitation using the radiation (hereinafter called recording light), a recording photoconductive layer exhibiting conductivity by being exposed to the recording light, a charge transport layer acting approximately as an insulator to an electric charge having the same polarity as an electric charge generated in the first electrode layer and acting approximately as a conductor to an electric charge having reverse polarity, a reading photoconductive layer exhibiting conductivity by being exposed to reading light (an electromagnetic wave for reading), and a second electrode layer (conductive layer) having transparency to the reading light, with these layers being disposed in this order. In the detector, a signal electric charge (latent image charge) representing image information is stored in a capacitor formed at an interface between the recording photoconductive layer and the charge transport layer.
In Japanese Patent Application Nos. 11(1999)-87922, 11(1999)-89553, and 11(1999)-207283, the applicant has proposed detectors each having a striped electrode in which a plurality of linear electrodes are laid out in a stripe-like shape as an electrode in the second electrode layer (electrode for light irradiation) having transparency to the reading light, and a plurality of linear sub-electrodes laid out in parallel to and in alternation with the linear electrodes comprising the stripe electrode in the second electrode layer in order to output an electric signal in accordance with the amount of the latent image charge stored in the capacitor.
By using a sub-electrode (electrode for outputting an electric charge) comprising the linear sub-electrodes in the second electrode layer, new capacitors are formed between the capacitor and each of the linear sub-electrodes. Therefore, it becomes possible to electrify the linear sub-electrodes with a transport electric charge having the reverse polarity of the latent image charge stored in the capacitor by recording, due to electric charge redistribution upon reading. In this manner, the amount of the transport electric charge to be distributed to each of the capacitors formed between the capacitor and the linear electrodes comprising the stripe electrode via the reading photoconductive layer can be reduced compared to the case of not using the linear sub-electrodes. As a result, the amount of the signal electric charge output from the detector to the exterior can be increased to improve reading efficiency. At the same time, fast reading response and efficient signal output can be realized.
However, if the linear electrodes comprising the stripe electrode and the linear sub-electrodes comprising the sub-electrode are laid out alternately in the second electrode layer, spacing between each of the linear electrodes and each of the linear sub-electrodes is substantially reduced, which may lead to short circuits between the stripe electrode and the sub-electrode due to a manufacturing defects or the like. If a short circuit occurs, the linear sub-electrodes do not serve as electrodes for improving reading efficiency. If one portion of the both electrodes becomes short-circuited, streaky noise appears in an image in the portion due to reduced reading efficiency caused by the short-circuit, although the reading efficiency itself improves due to the existence of the linear sub-electrodes.
The present invention has been conceived based on consideration of the above problems. An object of the present invention is therefore to provide an image detector not causing the short circuit between the linear electrodes and the linear sub-electrodes.
An image detector of the present invention has an insulator layer outside a second electrode layer so that an electrode layer for light irradiation (within the second electrode layer) and a charge output electrode face each other via the insulator layer.
In other words, the image detector of the present invention is an optical-reading type image detector and comprises a first electrode layer having transparency to recording light representing image information, a recording photoconductive layer exhibiting conductivity by being exposed to the recording light, a reading photoconductive layer exhibiting conductivity by being exposed to reading light, and a second electrode layer comprising a plurality of linear electrodes having transparency to the reading light and laid out in a stripe-like shape, with these layers being disposed in this order. A capacitor is formed between the recording photoconductive layer and the reading photoconductive layer. In this image detector, an insulator layer having transparency to the reading light is disposed outside the second electrode layer, and a plurality of linear sub-electrodes for outputting an electric signal in accordance with the amount of a latent image charge stored in the capacitor are laid out in a stripe-like shape outside the insulator layer, each of the linear sub-electrodes being laid out alternately with the linear electrodes in the second electrode layer. An electrode comprising the linear sub-electrodes is a sub-electrode (charge output electrode).
xe2x80x9cOutside the second electrode layerxe2x80x9d refers to a side of the second electrode layer opposite to the reading photoconductive layer, and xe2x80x9coutside the insulator layerxe2x80x9d refers to a side of the insulator layer opposite to the second electrode layer.
xe2x80x9cBeing laid out alternatelyxe2x80x9d refers to the case where the linear electrodes in the second electrode layer and the linear sub-electrodes are placed alternately via the insulator layer. A portion of the electrodes may overlap in a direction of electrode disposition.
The xe2x80x9cinsulator layer having transparency to the reading lightxe2x80x9d refers to the fact that the insulator layer has transparency to the reading light at least in a portion corresponding to the linear electrodes in the second electrode layer, in the direction of the linear electrode alignment. Therefore, an entire area of the insulator layer does not necessarily have transparency.
In order to cause the insulator layer to have transparency to the reading light, SiO2, SiC, and SiN are preferably used, for example.
According to the image detector of the present invention, the insulator layer having transparency to the reading light is disposed outside the second electrode layer, and the linear electrodes for light irradiation and the linear sub-electrodes for charge output face each other via the insulator layer. Therefore, thickness of the insulator layer can be set freely to some degree so that the electrode for light irradiation and the charge output electrode are not short-circuited. In this manner, short circuiting of the two electrodes can be prevented with certainty.
Furthermore, since the thickness of the insulator layer can be set to a thickness which does not cause the two electrodes to short-circuit, a distance between the two electrodes can be made smaller to some degree, and reading efficiency the same as in the case of the two electrodes being laid out alternately within the second electrode layer can be maintained.
Moreover, since the linear sub-electrodes are located outside the insulator layer, an electrostatic latent image is not erased due to an electric charge poured from the linear sub-electrodes.